1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method, and more particularly to an ink jet printing apparatus which performs a marginless printing. In the concrete, a marginless printing is printing an image on a print medium without leaving a blank margin at least one end (edge) portion of the print medium. Further, the present invention relates to an ink jet printing method which controls the number of nozzles used for the marginless printing at an edge portion of the print medium where there is a large transport error.
2. Description of the Related Art
In a serial type ink jet printing apparatus which prints an image on a print medium by repeating a printing scan of a print head and a line feed (or paper feed) alternately, it is difficult to print on a front or rear end portion of the print medium because of the print head scan and line feed. In recent years, however, the printing on the front or rear end portion of a print medium has become possible by using only a part of the nozzles arrayed in the print head for printing and by repeating a small line feed and a small-width printing scan. Printing apparatus capable of such a marginless printing have been available.
In the marginless printing (or margin-free printing), an ink absorber with its width corresponding to a length of a nozzle column in the print head is provided to a platen rib to absorb ink that is ejected outside a print medium due to print medium transport and cutting errors, thus preventing an interior of the apparatus or a back side of the print medium from being contaminated or smeared.
As shown in FIG. 9, a front end area of a print medium is printed by repetitively alternating a printing scan using four nozzles, counting from the end of the nozzle column, and a small line feed of about one nozzle. Repeating this printing scan followed by the small line feed several times completes the printing on the front end area of the print medium. After this, the number of nozzles used for printing is increased according to the line feed distance. In this example, the number of nozzles used for printing is increased by three nozzles at a time (added nozzles are marked with X in the figure).
However, in this marginless printing that uses only a part of the nozzles in the nozzle column, the ink state in those nozzles being used and the ink state in the remaining nozzles not used greatly differ. Particularly, in a bubble-through type ink jet printing apparatus which applies heat to ink in the nozzles by heaters to generate bubbles in the ink and thereby expel ink droplets, the ink state in the nozzles has great effects on the ink ejection.
In the example case of FIG. 9, the ink in the four nozzles that have been used from the beginning is kept hot and low-viscous and thus their ejection state is stable. As to the nozzles that were brought into operation from the middle of the printing process (nozzles marked with X in the figure), because they were put out of operation, the ink in these nozzles is cold and somewhat dry and their ejection is unstable. Therefore, the nozzles that began to be used from the middle of the printing process cannot produce a good printed result and may degrade a quality of that portion of an image printed by these nozzles (in the figure, a printed portion S).
In addition to the marginless printing, a printing method that similarly limits the use of nozzles has also been proposed for maintaining an image quality at an area near the front end area of a print medium. The printing method, which limits the use of nozzles according to the position of an area of the print medium being printed as described above, is also necessary in an ordinary margined printing to maintain a good image quality. This method, however, has a problem that the nozzles that were kept out of use may produce an unstable ink ejection during their first scan immediately after they are allowed to be used, causing a possible image impairment, which in turn leads to an image quality degradation.
As described in Japanese Patent Application Laying-open Nos. 8-336962 (1996) and 10-016228 (1998), a method has been proposed which energizes heaters with such a short electric pulse as will not cause an ink ejection and thereby heats the ink in the nozzles to keep it at an elevated temperature. This method, however, is based on the assumption that an ordinary printing using all the nozzles in the nozzle column is to be performed, and is designed to prevent a temperature fall of the ink in the nozzles which may occur during a low duty printing or during a printing in a low temperature environment. This method does not consider the problem associated with the printing of the front end area of a print medium at all.